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Subject[PATCH v2 2/2] mm, memory_hotplug: test_pages_in_a_zone do not pass the end of zone
From: Mikhail Zaslonko <>

If memory end is not aligned with the sparse memory section boundary, the
mapping of such a section is only partly initialized. This may lead to
VM_BUG_ON due to uninitialized struct pages access from test_pages_in_a_zone()
function triggered by memory_hotplug sysfs handlers.

Here are the the panic examples:
kernel parameter mem=2050M
page:000003d082008000 is uninitialized and poisoned
page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
Call Trace:
([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160)
[<00000000008f15c4>] show_valid_zones+0x5c/0x190
[<00000000008cf9c4>] dev_attr_show+0x34/0x70
[<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
[<00000000003e4194>] seq_read+0x204/0x480
[<00000000003b53ea>] __vfs_read+0x32/0x178
[<00000000003b55b2>] vfs_read+0x82/0x138
[<00000000003b5be2>] ksys_read+0x5a/0xb0
[<0000000000b86ba0>] system_call+0xdc/0x2d8
Last Breaking-Event-Address:
[<0000000000385b26>] test_pages_in_a_zone+0xde/0x160
Kernel panic - not syncing: Fatal exception: panic_on_oops

Fix this by checking whether the pfn to check is within the zone.

[ separated this change from]
Reviewed-by: Oscar Salvador <>
Tested-by: Gerald Schaefer <>
Tested-by: Mikhail Gavrilov <>
Signed-off-by: Mikhail Zaslonko <>
Signed-off-by: Michal Hocko <>
mm/memory_hotplug.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 07872789d778..7711d0e327b6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1274,6 +1274,9 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
if (i == MAX_ORDER_NR_PAGES || pfn + i >= end_pfn)
+ /* Check if we got outside of the zone */
+ if (zone && !zone_spans_pfn(zone, pfn + i))
+ return 0;
page = pfn_to_page(pfn + i);
if (zone && page_zone(page) != zone)
return 0;
 \ /
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